1. Field of the Invention
The present invention relates to the control of the link power in a mobile communications system, specifically, to a method and device for testing the link power control in a mobile communications system, which is able to test the transmission/reception power control between a base station and mobile even in a laboratory.
2. Discussion of Related Art
In a mobile communications system, when a transmitter transmits a radio wave, the radio wave passes through various transmission paths of air, ionosphere and the surface of the earth, and then it is received by a receiver. The reception sensitivity is, generally, in inverse proportion to four squares of the distance between the transmitter and receiver. Thus, when the distance between a transmitter and receiver A is 1 Km, and the distance between the transmitter and receiver B is 2 Km, the difference in the reception sensitivity between receivers A and B is 1/16.
Mobile units communicating with a base station perform the power control, to solve Near-Far problem. In order to remove the difference in the reception sensitivity according to the distance between the transmitter and receiver in the mobile communications system, the base station and mobile have the power control inducing function which controls the transmission/reception power to make the normal call possible when the normal call on the forward link and reverse link on the talking path becomes difficult after the call is set, due to various surrounding effects.
In a prior art, to test the normal operation state of the power control inducing function, the mobile is moved farthest in the region of the base station, and the received power of the mobile is checked as shown in FIG. 1. When the transmission/reception power control is required since the distance between the base station and mobile is changed, the contents of the communication between the mobile and base station are actually analyzed in the field, so as to produce the error rate of received data.
A conventional forward link power controlling method is disclosed in U.S. Pat. No. 5,461,639, in which a mobile periodically requests a base station to change the output power, and the base station sends a frame to the mobile at a specific rate. If the mobile receives the frame correctly, it sets a power control bit in the next frame to be transmitted to the base station. Based on the error rate of the received power control bits, the base station determines whether to increase or decrease the transmission power.
In the conventional method, the mobiles are tested outside the laboratory when the test of the power control inducing function of the mobile communications system is required. Accordingly, expensive and heavy testing devices and their operators should moved with the mobile. This deteriorates the efficiency in the testing operation, and costs much.